The file system's functions contained in the existing operating systems are responsible for organizing persistent contents required by the systems, applications and the final users, storing the contents in a local storage device, and providing such functions as reading, modifying, deleting and transferring the persistent contents under control of access permissions. With the development of storage and network technologies, file systems are greatly changed in terms of its composition and base for implementation.
The prior art has provided a distributed file system that stores multiple copies of each block of a file that is under its management, so as to ensure reliability of the file contents. As long as any copy is valid in the entire system, the data represented by that copy is valid, and a user can successfully access to the data. The reliable manner provided by independent copies belongs to the parallel system amongst reliability models. The parallel system is a system of enhanced reliability for providing reliability in parallel.
However, in order to ensure higher reliability, the aforementioned prior-art technology divides a file into blocks and subsequently stores the blocks in a plurality of data storage servers in direct redundancy mode, whereby the storage space utilization becomes low, thus bringing about high cost for system construction. Specifically when individual data storage server costs much, direct redundancy causes higher cost such that it is difficult to construct the system.